docs: def set_experiment_winner(experiment):
      """Mark an alternative as the winner of the experiment."""
      redis = _get_redis_connection()
      experiment = Experiment.find(redis, experiment)
      if experiment:
          alternative_name = request.form.get('alternative')
          alternative = Alternative(redis, alternative_name, experiment.name)
          if alternative.name in experiment.alternative_names:
              experiment.winner = alternative.name
      return redirect(url_for('.index'))